Construction and method of an electric motor drive

ABSTRACT

In an electric motor drive, a asynchronous motor, such as drum motor, has a stator ( 2 ) mounted on a non-rotatory shaft ( 1 ) and has rotatory, like by means of bearings ( 3 ), connected rotor ( 4 ), is arranged to drive the machine construction (actuator). The rotor ( 4 ) of the asynchronous motor conveyor&#39;s is arranged to be directly a functional part of the machine construction (actuator), like conveyor&#39;s ( 5 ) driving roll ( 5   a ). Also the rotor can be formed as a shell of pulley ( 4 ) which is part of a vacuum belt conveyor comprising a stationary vacuum box ( 11 ), the rotor drive further including a non-rotatory shaft ( 1 ) supported by at least one supporting bracket ( 8 ) which is connected to the vacuum box.

The object of this invention is the construction in electric motor drive, where an asynchronous motor, such as drum motor or similar motor, which has a stator mounted on a non-rotatory shaft and around the stator is a rotor, which is rotatory, like by means of bearings, connected on the same shaft and has a short-circuit arrangement, is arranged to drive a machine construction (actuator)

Above described types of asynchronous, compact drum motors have been presented for example in publications E 0 582 563,

U.S. Pat. No. 4,868,436 and FI 811414. Among these, the first-mentioned solution is carried into effect by keeping separate and individual copper short-circuit bars in their position by pressing them in place with collars mounted on the end flanges of the motor.

The disadvantage of this type of solution is the poor heat transmission from the short-circuit bars to the rotor shell. Further in the solution of U.S. Pat. No. 4,868,436 the rotor structure is built up of so called active part i.e. electric plate package and at least two separate rotor shell parts i.e. support flange and onto it by means of screw coupling connected rotor shell, which makes the solution in question unnecessarily complicated. In application publication EP 0 617 155 there is a much similar solution (of above mentioned U.S. patent), where motor's rotor package, which is constructed/laminated of electric plates, is connected together with it's short-circuiting conductors to drum roller by means of screw/press coupling, which operates as a roll surface. Also this solution is disadvantageous especially in manufacturing. Further in latter Finnish patent application is presented a drum motor, which is designed especially for elevator purposes. In this solution a separate roller with cable grooves and brake surface area for elevator's lifting cables and brakes is mounted on the upper shell of the rotor. E.g. in this solution is additionally proposed that the motor cooling is taken care of by machining radial ventilation holes in the roller and stator and to blow the cooling air to the holes with a separate blower.

To all of the above mentioned solutions it is common, that first of all respectively used machine construction (actuator)'s connection to the drum motor requires special mounting arrangements and/or extra parts for it i.e. a separate drive roll to be assembled on to an electrical motor's rotor (EP 0 582 563), a firmly assembled flange arrangement on the motor's frame (U.S. Pat. No. 4,868,436) or a shell to be assembled outside the drum motor (FI 811414 and EP 0 617 155 A1). On the other hand in the motor constructions in the above mentioned innovations the cooling circulation is carried out by traditional means, thus it is not possible to reach higher outputs than with standard drum motor solutions.

The purpose of the construction of this invention is to overcome the above-described disadvantages and thereby essentially improve the level of the technique in this area. It is principally distinctive to the construction according to this invention, to carry out this purpose, that the functional part of the machine construction (actuator), like conveyor's driving roll or similar, is arranged to operate by having short-circuit arrangement as the rotor of the asynchronous motor. In other words: the “actuator” (e.g. driving roll) is formed to constitute itself the rotor of the asynchronous motor, with the actuator comprising the short-circuit arrangement.

The construction according to the invention is characterized by that the functional part of the machine construction (actuator) like conveyor's driving roll, is arranged to operate by having short-circuit arrangement as the rotor of the asynchronous motor.

It should be noted that the term “actuator comprising the short-circuit arrangement” is referring to many various (or different) embodiments. In the most simple embodiment, the actuator is formed as a one-piece solid roll shell being free from short-circuit bars and rings (also being free from laminated elements).

In another embodiment (also being free from laminated elements) short-circuit bars and rings are provided. Each of the bars and the rings will be located within the roll shell, preferably when a tight or positive fit (or locking) being provided between each bar and the roll shell, whereby additional mounting elements (e.g. collars and/or screws) are no more needed.

The most important advantages of the construction of this invention is the simplicity of its construction, manufacturing and usage, efficiency and reliability of working, which attain the most possible integrated and compact machine configuration, which allow to get higher output and higher torque from the used asynchronous massive rotor and significantly to improve its performance in other ways too. The simplicity of the construction of this invention as advantageous solution is based e.g. on face there is no need to use traditional short-circuiting conductors, as the short-circuit arrangement is established directly into the functional part of the machine construction (actuator), like conveyor's driving roll. On the other hand the structure of this invention makes it possible to use the traditional short-circuiting connectors in a new way, so that they are located essentially internally on a functional part of the machine construction (actuator) as the rotor shell, like conveyor's driving roll. When applying advantageously the structure of this invention, the asynchronous motor is equipped with primary and secondary cooling circulation to cool both the stator and the rotor for example so that the cooling fluid is firstly essentially carried through the stator shaft and with the help of the holes in the shaft elsewhere as parallel flow through the flow system in the rotor shell. As a further improvement the rotor is manufactured of electric conductive compound metal structure, where copper short-circuit bars or pipes and rings are for example explosion welded into pre-drilled/machined holes/slots. On the other hand during manufacturing of the asynchronous motor it is possible to utilize also a casting technique.

Further advantageous solution is to assemble the stator on the hollow shaft/pipe also working as stator shaft, which is used for example to feed over-pressure cooling air. Herewith it is effectuated a hermetic primary cooling, which is known from EP 0 617 155 and which prevents dirt to penetrate into the drum motor, which is not possible to prevent with the conventional effectuated freely (open) breathing air-cooled solutions. Further advantageous feature is that the short-circuit hollow bars or pies are positioned within the rotor shell, functioning as secondary cooling channels. Thereby it is possible to carry the cooling air to the hottest spots of the rotor, which helps in its way significantly both to obtain the maximum output and to increase the amount of starts/stops of the machine construction (actuator) equipped with the motor in question.

The advantageous solutions of the structure of the invention have been presented in separate independent patent claims.

Object of this invention is also a method for equivalent purpose, which is more specifically described in independent patent claim's introduction section and whose characteristic features in corresponding patent claim's characteristic section

The method according to the invention is characterized by that the functional part of the machine construction (actuator), like conveyors driving roll, is arranged to operate by having short-circuit arrangement as the rotor of the asynchronous motor.

One of the most important advantages the method of this invention has, is the simplicity of the operating principle and the simple constructions which makes it possible and the reliability of working and which allows to gain the utmost compact machine construction (actuator) unit with integrally united asynchronous motor to achieve high mechanical load capacity, vibration strength and high starting and operation torque features. The simplicity of the method of this invention as a advantageous solution is based for example on the fact that there is no need to use a separate laminated rotor component with traditional short-circuiting conductors inside a functional part of the machine construction, by establishing a short-circuit arrangement directly into the functional part of the machine construction (actuator), like conveyor's driving roll. On the other hand the method of this invention makes it possible to use the traditional short-circuiting connectors in a new wavy so that they are located essentially internally on a functional part of the machine construction (actuator) as the rotor shell, like conveyor's driving roll.

Furthermore as an advantageous development of this innovation, it is possible to increase an air gap diameter between stator and rotor once a maximum outer diameter and total length of a drum motor is limited. Thus by this innovative design it is possible to get higher output power and higher torque compared to an asynchronous drum motor having same main dimensions as this new innovative drum motor construction and having a standard laminated rotor component inside a rotor shell.

Furthermore as an advantageous development of this method is to minimize the manufacturing costs of the here mentioned massive motor for example by manufacturing the rotor and the associated slots by casting them of steel.

Applying the method advantageously the asynchronous motor is being cooled effectively to get higher output than with conventional ones can be reached, because correctly carried out i.e. according to this invention realized for example hermetic and essentially in axial direction trough the asynchronous motor carried cooling fluid flow makes it possible for example to direct the over-press cooling air to the hottest spots of the rotor, which is an essential condition both to increase the maximum output and to increase the amount of starts/stops. On the other hand compared to the freely breathing air-cooled solutions this solution prevents especially in hard conditions filth to penetrate into the drum motor structure.

Cooling of asynchronous motor with a solid rotor can be realised either with or without a secondary cooling arrangement via hollow bars or tubes inside a functional part of the machine construction (actuator) as the rotor shell. In such constructions the cooling is taken care of only with a primary cooling arrangement (e.g. air flow arrangement though an air gap between an inner surface of rotor shell and an outer surface of stator component.

Furthermore it is important that the short-circuit bars and rings belonging advantageously to the short-circuiting adjustment are arranged essentially integral with rotor shell i.e. at least partly or then totally with internal arrangements, and thus also a much more efficient heat conduction than present, between the steel shell and the copper short-circuit bars and rings can accomplished than with the traditional solutions. This also gives better possibilities for higher output and to increase the starts and stops of the asynchronous motor within a certain time interval.

Advantageous solutions of the method of the invention have been presented in separate independent patent claims.

The invention is in more detail presented in the description and the attached drawings.

FIG. 1 presents a longitudinal cross section of a typical machine construction (actuator) unit, which is accomplished with the method in this invention and

FIG. 2 presents a cross-profile of spots FIG. 2-FIG. 2. in FIG. 1.

FIGS. 3 a-3C present some alternative massive motor constructions of a drum motor.

FIGS. 4 and 5 present a drum motor designed according to the invention and integrated to one end of a vacuum belt conveyor construction, with FIG. 5 being a section along line V-V of FIG. 4.

Referring to FIGS. 1 to 3, the object of this invention is a construction in electric motor drive, where a so called solid asynchronous motor, which has a stator 2 mounted on a non-rotatory shaft 1 and around the stator is a rotor 4, which is, like by means of bearings 3, rotary connected on the same shaft 1 and has a short-circuit arrangement, is designed to drive a machine construction (actuator). The functional part of the machine construction (actuator), like conveyor's 5 driving roll 5 a or 5 b or 5 c is designed to operate by integrally connected short-circuit arrangement as the rotor 4 of the asynchronous motor. Especially in FIG. 3 c is shown the most simple structure of the invention in which conveyor's driving roll 5 a is realized with a solid shell, which operates directly as the short-circuit arrangement or the rotor 4 without any traditional laminated rotor component with short-circuit conductors (e.g. short-circuit bars and rings). The solution according to this principle is also shown in FIG. 3 b, where driving roll 5 b is designed to operate as the rotor of the asynchronous motor with the solid shell having on its inner surface drilled or machined holes or grooves.

Different from FIGS. 2 b and 3 c, the invention may be advantageously used in connection with the structure, where the short-circuit arrangement can be realize in the rotor's shell 4 a with short-circuiting conductor bars 4 b and rinds 8. In this connection short-circuiting connector bars 4 b and rings 18 are arranged to operate at least partly internally of the rotor's shell 4 a operating as functional part of the machine construction (actuator), such as conveyor's driving roll 5 c. This type of solutions are presented especially in FIG. 2, where round short-circuit bars 4 b are being used and in FIG. 3 a where quadrangular short-circuit bars 4 b, are being used in rotor shell 4 a′. The bars 4 b shown in FIG. 2 may be hollow, so that each bar comprises a channel 4 c for piping cooling fluid. At each end of shell 4 a, a flange 7 is provided which connects the shell to one of the bearings 3.

In FIG. 3 a is shown a design, where conveyor's driving roll 5 a is realised by a solid shell having quadrangular short-circuit bars on its inner surface. This type or electrical rancor design should be used when a compact drum motor constructions (e.g. maximum outer diameter and total length of the drum motor are limited) with high output power and torque are desired. Such a compact drum motor is needed in vacuum belt conveyors used for “tail threading” in paper machines.

A typical design of drum motor's stator component 2 consists typically a pile of 0.3-1.0 mm thick electrical sheets 21 which are mounted on a stationary hollow shaft and fixed at their position by spot welding stator end plates 20 to the stationary shaft. Stator windings 6 are connected via electrical connection cable 19 to an external electric grid.

FIGS. 4 and 5 show one end of a vacuum belt conveyor comprising an endless air pervious belt 10 which in operation—travels across two rotary pulleys, only one pulley 4 being shown. The pulleys are supported by a vacuum box 11. Therein a negative pressure will be created by any vacuum source (not shown). The negative pressure will propagate through openings 12 of a cover plate 13 and through belt 10 in order to convey a web of paper or similar material, in particular a lead strip or “tail” which has been separated from threading purposes (see e.g. U.S. Pat. No. 3,355,349).

In order to drive the belt 10, a pulley 4 is designed as the rotor of an electric motor drive according to the present invention. Similar to FIG. 1, a stationary hollow shaft 1 supports a stator 2 and (by means of bearings 3) the rotor 4,—which is the pulley of the vacuum belt conveyor—and which again comprises a rotor shell 4 a and two end-flanges 7.

Preferably, the following measures may be provided in order to adapt the electric motor drive to the demands of a vacuum belt conveyor:

The width W of conveyor 5 (and also the length L of the pulley's shell 4 a should be relatively small, about 0.25 m. The pulley's diameter should preferably be less than 0.15 m. On the other hand, the speed of the belt should be about the same as the operating speed of modern paper machines which may exceed 2000 m/min. Therefore, there is a need for very high motor output while the dimensions of the motor drive should be relatively small.

To fulfil these demands, the distance D between the bearings 3 is larger than the length L of the pulley's shell 4 a, in order to increase the internal space being available for stator 2 and for the short-circuit arrangement of the rotor 4. As a consequence, each flange 7 is formed as a bushing which bridges the difference between length L and distance D. Furthermore, each of the supporting brackets 8 which connect the stationary shaft 1 to the side walls of the vacuum box 11 is formed similar to a Z (in other words: it is “double folded”). In addition, each support bracket 8 mays be wrapped around the periphery of one of the flanges 7.

In order to improve the cooling effect, the hollow shaft 1 comprises at one of its ends an internal (e.g. coaxial) supply channel (15) as well as a discharge channel 16, as a result, all the cooling fluid X must pass the inner side of stator 2 as well as its outer side and the inner side of the rotor (plus the channels 4 c, if existing, in the bars 4 b in FIG. 1).

Also, the following is advantageous: The above mentioned supporting brackets 8 can be used also as a connection surface for vacuum belt conveyor's accessories (e.g. knife plates, rotary rippers and choppers) (which is not shown as practical solution in enclosed drawings).

In addition to the things mentioned above, the cooling of the machine construction (actuator) operating as a rotor of a asynchronous motor is realized advantageously mainly with primary cooling by carrying over-press cooling air X in axial direction through the stator shaft 1, which can be for example a hollow shaft, pipe or similar and it is equipped with it's first flow arrangement 1 a. On the other hand when using advantageously the structure of this invention it is possible to boost the cooling of the asynchronous motor besides what was described earlier or instead of it also with secondary cooling by equipping the short-circuiting bars 4 b′ with another flow arrangement 4 c. Then, for example, it is possible to carry cooling air X in axial direction through the hollow copper short-circuit bars 4 b, for example, according to the principle in FIG. 1 with the help of the holes 1 b in the stator shaft 1 together with the primary air flow 1 a which take place together with the parallel flow to the hottest sports of the rotor, which helps to get higher output from the machine construction (actuator) and especially to improve to carry the short run starts/stops.

Once an asynchronous motor has a solid rotor's cross section as shown in FIGS. 3 a, 3 b and 3 c, cooling is taken care of an air flow arrangement through an air gap which locates between an inner surface of a rotor shell 5 a, 5 b, 5 c and an outer surface of stator component 2.

Further advantageous solution of the structure of the invention is to manufacture the rotor of electric conductive compound metal stricture, where copper short-circuit bars 4 b; 4 b′ are integrally connected to the steel rotor shell 4 a; 4 a′ for example by explosion welding or by centrifugal casting.

It is possible with the asynchronous motor realized according to the invention when using especially star type coupling for windings, to get the output of the drum motor equipped with three, four, or six pole stator windings always reach the level 0.5-500 kW and to have the speed of rotation typically in the area of 0-20000 rpm.

As a further advantageous development (which is not shown in enclosed drawings) it is advantageous to benefit the frequency transformer used by the asynchronous motor, which is equipped with active rotation speed control. In this connection rather traditional solutions can be used to achieve the wanted effect.

The object of this invention is also a method with an electric motor drive, where the machine construction (actuator) is used by a asynchronous motor, such as drum motor, which has a stator 2 mounted on a non-rotatory shaft 1 and around the stator is a rotor 4, which is rotatory, like by means of bearings 3, connected on the same shaft 1 and has a short-circuit arrangement. The functional part of the machine construction (actuator), like conveyor's 5 driving roll 5 a, is arranged to operate by having short-circuit arrangement as the rotor 4 of the asynchronous motor (typical constructions shown in FIGS. 2 and 3 a). The method according to this principle is applied in simplest way for example in constructions in FIG. 3 b, wherein driving roll's 5 b machined grooves/slots 5 d are arranged as the short-circuit arrangement. On the other hand in FIG. 3 c is a similar type of solution without traditional short-circuit bars, wherein the driving roll 5 a is realized a solid shell, which operates directly as the short-circuiting arrangement.

Furthermore as an advantageous application of this method it is advantageous to benefit it with asynchronous motor, whose short-circuit arrangement is connected to the rotor 4, like short circuiting bars 4 b and rings 8 are supported on rotor's shell 4 a. In this connection short-circuit bars and rings belonging to the short-circuit arrangement are arranged to operate at least partly internally as the rotor's 4 shell 4 a of the operating functional part of the machine construction (actuator), such as conveyor's driving roll 5 a. In this connection this type of solution is presented, especially in FIG. 2, showing round short-circuit conductors 4 b and further in FIG. 3 a showing quadrangular short-circuit bars 4 b′.

Furthermore referring to FIG. 1 this method can be used with an asynchronous motor which is arranged to be cooled by having a fluid flow. The cooling of the asynchronous motor is realized as a closed system by carrying cooling fluid, such as over-press cooling air X, hermetically essentially in axial direction in a primary flow arrangement 1 a through the stator shaft 1 like hollow shaft, pipe or similar. On the other hand the cooling of the asynchronous motor can be arranged instead of as described above by carrying cooling fluid, such as over-press cooling air X hermetically essentially in axial direction in a secondary flow arrangement 4 c provided in short-circuit conductors 4 b like hollow bars or pipes.

Especially referring to FIG. 1, as an example: Rotor 4 of the solid asynchronous motor is manufactured of electric conductive compound metal structure, when advantageously, for example, copper short circuit bars 4 b which are welded, like explosive welded or butt welded into the holes in the steel rotor shell 4 a or that they are cast integral with a most suitable casting method, like press casting method (solution is not presented in FIG. 1). With above mentioned methods every short-circuit bar 4 b and ring 18 is integrated as an integral part of rotor shell 4 a, which allows to achieve better heat transmission between the steel shell and copper short-circuit conductors. This fact has a great importance when trying to get higher maximum power from the machine constructions (actuators) than with traditional solutions and especially when short run starts/stops are in question. The same is true with the embodiment shown in FIG. 3 a comprising rotor shell 4 a′ and bar 4 b′.

It is obvious that this invention is not limited to the above mentioned or explained solutions, it can be considerably modified within it's basic idea. Thereby it is possible firstly to utilize the construction or arrangement of this invention in most different connections, whereupon the dimensions and constructions can considerably differ from the hereby presented example drawings. On the other hand other type of fluids can be used in the cooling of the asynchronous motor realized according to the invention or the cooling can be done differently from what presented above. 

1-16. (canceled)
 17. An electric motor drive, comprising: a stator; a hollow non-rotary shaft carrying said stator; a plurality of bearings connected to said non-rotary shaft; a rotor rotatably positioned around said stator, said rotor being rotatably carried by said bearings; and a machine actuator having a functional part with a short circuit arrangement associated with said rotor for operating said actuator, said short circuit arrangement being at least one of hollow and solid short circuit conductors explosion welded to said rotor.
 18. The electric motor drive of claim 17, wherein said short circuit means is said rotor.
 19. The electric motor drive of claim 17, further comprising a conveyor driving roll, wherein said functional part is said conveyor driving roll.
 20. The electric motor drive of claim 17, further comprising: a conveyor driving roll, said functional part being said conveyor driving roll; a plurality of short circuiting bars; and a plurality of rings, said short circuiting bars and said rings being arranged integral with said rotor; wherein said short circuiting bars and said rings are said short circuit arrangement.
 21. The electric motor drive of claim 17, wherein said rotor is an electrically conductive compound metal structure including at least copper short circuit conductors which are attached to said rotor by one of explosive welding, butt welding into holes in said rotor and integral with the casting of said rotor.
 22. The electric motor drive of claim 17, wherein said stator includes a winding, and further comprising star type couplings utilized in said winding of said stator, wherein said winding includes one of a three pole stator winding, a four pole stator winding and a six pole stator winding, wherein said motor has a power output from approximately 0.5 kilowatt to approximately 500.0 kilowatt, and wherein said motor has a rotational speed of approximately 0 rpm to approximately 20,000 rpm.
 23. The electric motor drive of claim 17, further comprising: a frequency transformer drive; and an active rotation speed control.
 24. A method of constructing an electric motor drive comprising the steps of: mounting a stator on a hollow non-rotary shaft; positioning a rotor around said stator; connecting said rotor to said non-rotary shaft with bearings; and incorporating a short circuit arrangement into said rotor, said short circuit arrangement being at least one of hollow and solid short circuit conductors explosion welded to said rotor; wherein said rotor is configured as a functional part of a machine actuator.
 25. The method of claim 24, wherein said short circuit arrangement is a plurality of rings and a plurality of short circuiting bars, said plurality of rings and said plurality of short circuiting bars arranged at least partially internal to said rotor.
 26. The method of claim 24 further comprising the step of forming said rotor into an electrically conductive compound metal structure including at least copper short circuit conductors which are attached to said rotor by one of explosive welding, butt welding into holes in said rotor and integral with the casting of said rotor. 